This invention relates to a pressure sensitive adhesive system for use in moldable automotive trim panels. Automotive trim panels are used to cover the hard surfaces of car interiors. Parts such as instrument panels, armrests, center consoles, seating, head rests, door skins and body pillar trim are some of the components provided with interior trim panels. These components typically comprise a structural substrate of aluminum, ABS or polypropylene. The surfaces are covered by a trim panel which typically has a vinyl or textile outer surface cushioned by a layer of foam padding underneath. The outer surface exposed to the vehicle passenger is referred to as an A-side layer. Typical materials for the A-side layer are leather, vinyl or textile materials such as cloth or carpet.
A desirable characteristic of a trim panel is that it have a padded or cushioned feel, for both styling and safety purposes. Also, for ease of installation, it is preferred that the trim panel be pre-formed to a contour that matches that of the underlying substrate to which the panel is applied. While the typical A-side materials have suitable qualities in terms of durability and appearance, none of them by themselves provide a padded or cushioned feel, nor can they be formed into a permanently contoured shape. Accordingly, a layer that provides padding and structure must be attached to the A-side material, such that it will lie between the substrate and the A-side layer. A suitable trim panel that is padded and formable to retain the contour of the substrate is described and claimed in U.S. patent application Ser. No. 08/797,643, now U.S. Pat. No. 5,962,089 invented by Vincent H-H. Jones and David L. Simon and in U.S. patent application Ser. No. 08/797,646, now U.S. Pat. No. 5,847,961 invented by Vincent H -H. Jones, David L. Simon and Scott M. Kloock, both filed on Jan. 31, 1997. The disclosures of these two applications are incorporated herein by reference.
The two patent applications describe a technique for thermoforming an automotive trim part formed of an A-side material laminated to a thermoformable foam layer. The material of the applications provides a self-supporting, padded trim panel, contoured to match a non-flat substrate and ready for attachment thereto. The present invention is directed to a construction for attachment of the trim panel to a substrate and is particularly concerned with a pressure sensitive adhesive which can be applied prior to the thermoforming of the part.
Pressure sensitive adhesive (PSA) systems comprise an adhesive layer covered by a removable release liner. These systems are also referred to as peel and stick adhesive systems. In general, PSA systems are not new. Bumper stickers, window decals, two-way tape and new postal stamps are all examples of PSA technology. The idea of using PSA for flat automotive trim panels is also known. There are many examples of substantially flat items of carpet, cloth, insulation and other trim pieces being applied to cars and trucks. While the performance requirements for automotive applications are more stringent than for a window decal (for example, the automotive component must withstand heat and cold cycles ranging from xe2x88x9230xc2x0 F. to +212xc2x0 F.), the general concept and methods of making the parts are essentially the same. In each case, a substantially flat adhesive layer and a release liner are applied to a substantially flat item. The end user or an assembly plant worker then removes the release liner and applies the item to its intended position, manipulates the part in place until it is properly located, and then applies pressure to wet-out the adhesive and adhere the part.
PSA represents a tremendous advantage to the automotive industry, particularly over hot-melt adhesives, for a number of reasons:
1. A PSA system eliminates xe2x80x9copen timexe2x80x9d as a factor in bond performance. Open time is the maximum amount of time an operator has available to complete the assembly of two or more components once the adhesive is ready for assembly;
2. No external heat source is required. A PSA system uses only normal ambient room temperature to secure components. This eliminates the potential for injuries resulting from the use of heat-activated processes like hot-melt adhesives;
3. PSA eliminates the need for adhesive dispensing equipment and the traditional application of adhesive at assembly. This also eliminates equipment such as robots, glue guns, etc., as well as environmental and safety issues sometimes associated with gluing operations;
4. PSA eliminates applying adhesive promoters to the back of a trim panel intended for use with a low surface energy substrate such as polypropylene. Such promoters are necessary to make traditional gluing systems work;
5. PSA technology allows for more consistent application of the adhesive layer, improving quality and allowing for the use of adhesives targeted at tough applications such as bonding to polypropylene. All of the above represent cost savings.
With all of the clear advantages, there is a strong desire for a PSA system for non-flat, contoured automotive trim panels which has heretofore not been satisfied. The reasons for this are as follows:
1. Lack of a PSA system which lends itself to being molded into a contoured shape;
2. Lack of a PSA system which will withstand the temperatures typically used in molding automotive trim components such as door bolsters. Such temperatures typically range from 300xc2x0 F. to 700xc2x0 F.;
3. Lack of a method for making dimensionally repeatable contoured automotive trim panels which has the tooling and process controls required for handling a PSA system; and
4. Lack of a method to manufacture a PSA system which can withstand items 1, 2 and 3 above.
The above difficulties have led to failures with PSA systems in contoured trim panels. These failures include the release liner wadding up, the part material getting stuck in the tooling, the release liner tearing during the molding process, and the PSA system being burned away during the molding process.
The present invention is directed to a pressure sensitive adhesive for moldable automotive trim materials and to a non-flat automotive trim part having the PSA system applied thereto.
The trim panel has an A-side layer laminated to a thermoformable layer. A pressure sensitive adhesive is applied to the thermoformable layer and covered by a release liner that can withstand the high heat of thermoforming. The part is then thermoformed at a temperature of at least about 300xc2x0 F. or at least about 350xc2x0 F. The release liner is preferably a polyester film with a differential release silicone treatment. That is, the polyester film has a silicone coating or layer on both sides, but one of the silicone layers has an inhibitor added so that the pressure sensitive adhesive sticks more tightly to that side than the other side. The silicone treated polyester film is said to have a xe2x80x9ctightxe2x80x9d side and a xe2x80x9cloosexe2x80x9d side. The pressure sensitive adhesive is applied to the tight side; the film can then be rolled up on itself and when it is unrolled, the adhesive will preferentially adhere to the tight side and release from the loose side. The pressure sensitive adhesive system can be applied to the thermoformable layer at the time the thermoformable layer is laminated to the A-side layer. Or, the PSA system could be applied separately from the lamination of the A-side and thermoformable layers.